1. Field of the Invention
The present invention is directed to rear combination lamps for automotive lighting systems.
2. Description of the Related Art
For many years, automobiles have employed electric lighting that serves a variety of functions. For instance, lights provide forward illumination (headlamps, auxiliary lamps), conspicuity (parking lights in front, taillights in rear), signaling (turn signals, hazards, brake lights, reversing lights), and convenience (dome lights, dashboard lighting), to name only a few applications. Historically, incandescent bulbs have been used for most or all lighting in an automobile, being available in a variety of sizes, shapes, wattages, and socket packages.
In recent years, light emitting diodes (LEDs) have started to appear in some of the lighting applications for automobiles. Compared with incandescent bulbs, LEDs use less power, last longer, and have less heat output, making them well suited for automotive applications.
In the relatively short time period since LEDs have been introduced as lighting sources, automakers have adopted a cautious position. While they have been eager to adopt LEDs for all of the advantages stated above, they have been hesitant to completely abandon the familiarity of a bulb/lamp with a socket and its accompanying traditional-style optics. As a result, in recent years there have been several lighting subsystems that have the mechanical feel of the old incandescent-style bulbs and fixtures, but actually use LEDs as their light sources.
FIG. 1 shows a typical automobile 1, with typical exterior lights that front turn indicators 2, include headlamps 3, fog lamps 4, side repeaters 6, a center high mounted stop lamp 7, a license plate lamp 8, and so-called “rear combination lamps” 9 (RCLs). Any or all of these may include accessories, such as a headlamp cleaning system 5. We concentrate primarily on the rear combination lamps 9 for this application.
Note that each rear combination lamp 9 may include a tail light (also known as a marker light), a stop light (also known as a brake light), a turn signal light, and a back up light. Each light in the rear combination lamp may have its own light source, its own reflection and/or focusing and/or collimation and/or diffusing optics, its own mechanical housing, its own electrical circuitry, and so forth. In this respect, an aspect or feature of one particular light may be used for any or all of the lights in the rear combination lamp 9. Optionally, one or more functions may be shared among lights, such a circuit that controls more than one light source, or a mechanical housing that holds more than one light source, and so forth. For instance, each lighting sub-system typically has its own independent lamp, although the tail light and stop light functions may be combined in a single lamp (bulb) having a double filament.
In recent years, as LEDs have started to appear in exterior automotive lighting systems, one trend is to integrate the LEDs closely into the fixture. For instance, the center high mount stop lamps 7, or CHSMLs, are now mostly done in this fashion as it was relatively easy to adapt an LED module to the application. Because of the long life of LEDs, this may be the favored approach over time.
In other words, in the long term, the light fixtures, including the housing, the reflectors, the lens cover and any intermediate optical elements, will most likely become adapted to a configuration that is designed optimally around the LED. The electrical connections, the heat sink, the collimation and/or reflection and/or diffusing optics will most likely have designs that are primarily suited to LEDs, rather than primarily to conventional incandescent bulbs or lamps and then modified to include LED light sources.
However, in the short term, many automakers prefer familiar and known technology, including known reflector and bulb geometries that were developed for incandescent lamps and have been used for many years. As a result, several lighting manufacturers have developed rear combination lamp systems that use LEDs as their light sources, but use conventional light set socket openings and traditional style optics. The lamp is accessible from the back, i.e., from the side opposite the viewer, as is conventional with older incandescent systems. These lamp systems are appealing to automakers in the short term because the mechanical aspects of the lamp systems are consistent with the older, established systems that use incandescent bulbs. An example of such a lamp system is the JOULE product, which is commercially available from Osram Sylvania, based in Danvers, Mass.
There have been various designs for these lamp systems that use LED sources but have the mechanical feel of the older incandescent systems. Each of these designs had some drawbacks, such as difficulty during assembly, or a low optical efficiency, caused by losses.
An example of one of these known designs is disclosed in U.S. Pat. No. 6,991,355, issued on Jan. 31, 2006 to Coushaine et al., and assigned to OSRAM Sylvania Inc., based in Danvers, Mass. In this design, various LEDs 22 are attached to one side of a printed circuit board 20, and a heat sink 25 is attached to the other side of the printed circuit board 20. The LEDs 22, circuit board 20 and heat sink 25 are all located outside a concave reflector 50, adjacent to the base (vertex) of the reflector. Light from each LED 22 is directed into the interior of the reflector 50 via a respective light guide 30 that extends from the LED 22 through a hole at the vertex of the reflector 50. The exiting face of each light guide 30 is located at the focus of the reflector 50, so that light emitted from an LED 22 enters the light guide 30, exits the light guide 30 at the focus of the reflector 50, reflects off the reflector 50 and emerges from the lamp as a collimated beam. One of the designs uses a curved light guide 30a, so that the exiting face of the light guide is oriented appropriately, and the light exiting from the light guide travels in a suitable direction and strikes the reflector 50 in a suitable location. Another of the designs uses a straight light guide 30 with an intermediate reflector 26 to direct the light guide output appropriately onto the reflector 50.
In the design of '355, the light guide 30 may be the source of loss. Typical light guides are largely cylindrical rods of plastic or glass, with all surfaces being smooth, or as smooth as possible for a molded component. There may be additional polishing steps performed on the part, but such polishing steps add undesirable expense to the light guide, and therefore, to the whole lamp unit.
The longitudinal faces of the light guide are the entrance and exiting faces, and both may introduce loss. For instance, if the faces are uncoated, there may be a reflection loss of about 4% per surface, due to the difference in refractive index between the rod and air. Such reflection loss may be reduced by applying anti-reflection coatings to the longitudinal faces, but this may add undesirable expense to the light guide, and, therefore, to the whole lamp unit. In addition, there may be additional losses at the longitudinal faces caused by scattering. Such scattering losses may be reduced somewhat by ensuring that the longitudinal faces are relatively smooth, but in practice, these scattering losses are difficult to eliminate.
The transverse face of the light guide is typically left uncoated, so that light propagating along the interior of the light guide experiences total internal reflection at each bounce off the exterior face. There may be scattering losses caused by surface roughness, contaminants, or other imperfections along the transverse face. As with the scattering losses from the longitudinal faces, the scattering losses from the transverse face may be difficult to eliminate.
Accordingly, it would be beneficial to provide a rear combination lamp that uses LEDs as its light source, inserts from the back of the lamp, and eliminates the optical losses and expense of a light guide.
Because the present application is directed to automotive lighting systems, it is beneficial to first review some terminology.
The parts that make up the lighting systems at the corners of vehicles are known as “light sets”. In buildings, the equivalent of “light sets” would be fixtures. A light set typically includes a plastic structure or housing, one or more reflectors, lens optical systems in some cases, and a lens cover usually fitting the exterior styling of the vehicle and often having colored sections, such as amber and red. The housing of the light set includes socket openings, usually in the rear, to receive and retain a socket with a lamp (commonly referred to in the U.S. as a “bulb”), venting means, and in some cases for forward lighting, adjuster means.
In general, there are four key elements for an LED-based lighting module: (1) the actual LED chip or die, (2) the heat sink or thermal management, which dissipates the heat generated by the LED chip, (3) the driver circuitry that powers the LED chip, and (4) the optics that receives the light emitted by the LED chip and directs it toward a viewer. These four elements need not be redesigned from scratch for each particular module; instead, a particular lighting module may use one or more elements that are already known. The following paragraphs describe several of these known elements, which may be used with the LED-based lighting module disclosed herein.
U.S. Pat. No. 7,042,165, titled “Driver circuit for LED vehicle lamp”, issued to Madhani et al., and assigned to Osram Sylvania Inc. of Danvers, Mass., discloses a known driver circuit for LED-based lighting modules, and is incorporated by reference herein in its entirety. In '165, a first vehicle lamp driver circuit for a light emitting diode (LED) array is disclosed, the LED array having a first string of four LEDs in series and a second string of four LEDs in series. A first LED driver drives the first LED string and a second LED driver drives the second LED string. In a STOP mode of operation, the current to both LED strings is controlled by the LED driver in series with the LED string. In a TAIL mode of operation, the current is provided to only one LED string via a series connected diode and resistor. When there is reduced input voltage, operation of the LED strings is provided by switching circuits that short-out one LED in each LED string. A second vehicle lamp driver circuit comprises a first LED string and a second LED string in series with a control switch having a feedback circuit for maintaining constant current regulation to control the sum of the current in each LED string and reduce switching noise. The driver circuit disclosed by '165 may be used directly or may be easily modified to drive the LED chip for the lighting module disclosed herein.
U.S. Pat. No. 7,110,656, titled “LED bulb”, issued to Coushaine et al., and assigned to Osram Sylvania Inc. of Danvers, Mass., discloses a complementary socket and electrical connector mechanical structure for LED-based lighting modules, and is incorporated by reference herein in its entirety. In '656, an LED light source has a housing having a base. A hollow core projects from the base and is arrayed about a longitudinal axis. A printed circuit board is positioned in the base at one end of the hollow core and has a plurality of LEDs operatively fixed thereto about the center thereof. In a preferred embodiment of the invention the hollow core is tubular and the printed circuit board is circular. A light guide with a body that, in a preferred embodiment, is cup-shaped as shown in FIGS. 2 and 4a, has a given wall thickness “T”. The light guide is positioned in the hollow core and has a first end in operative relation with the plurality of LEDs and a second end projecting beyond the hollow core. The thickness “T” is at least large enough to encompass the emitting area of the LEDs that are employed with it. The complementary socket and electrical connector mechanical structure disclosed by '656 may be used directly or may be easily modified for the lighting module disclosed herein.
U.S. Pat. No. 7,075,224, titled “Light emitting diode bulb connector including tension receiver”, issued to Coushaine et al., and assigned to Osram Sylvania Inc. of Danvers, Mass., discloses another complementary socket and electrical connector mechanical structure for LED-based lighting modules, and is incorporated by reference herein in its entirety. In '224, an LED light source (10) comprises a housing (12) having a base (14) with a hollow core (16) projecting therefrom. The core (16) is substantially conical. A central heat conductor (17) is centrally located within the hollow core (16) and is formed from solid copper. A first printed circuit board (18) is connected to one end of the central heat conductor and a second printed circuit board (20) is fitted to a second, opposite end of the central heat conductor (17). The second printed circuit board (20) has at least one LED (24) operatively fixed thereto. A plurality of electrical conductors (26) has proximal ends (28) contacting electrical traces formed on the second printed circuit board (20) and distal ends (30) contacting electrical traces on the first printed circuit board (18). Each of the electrical conductors (26) has a tension reliever (27) formed therein which axially compresses during assembly. A cap (32) is fitted over the second printed circuit board (20); and a heat sink (34) is attached to the base and in thermal contact with the first printed circuit board. As with '656, the complementary socket and electrical connector mechanical structure disclosed by '224 may be used directly or may be easily modified for the lighting module disclosed herein.
U.S. Pat. No. 6,637,921, titled “Replaceable LED bulb with interchangeable lens optic”, issued to Coushaine, and assigned to Osram Sylvania Inc. of Danvers, Mass., discloses a reflective optic that can receive light from an LED, emitted perpendicular to a circuit board, and reflect it in a number of directions, all roughly parallel to the circuit board. The optic disclosed by '921 may have the shape of an inverted cone, with the point of the cone facing the LED chip. The cone may be continuous, or may alternatively have discrete facets that approximate the shape of a cone. The reflective optic may be used with a single LED chip, or multiple LED chips arranged around the point of the cone. The reflective optic disclosed by '921 may be used with the LED-based lighting module disclosed herein, and may be disposed in the optical path between the LED chip and the reflector that directs the LED light towards a viewer.